Field of the Invention
The present invention relates to a filtration system, and, in particular, to an underdrain with an underdrain wall adaptor for controlling air and water passage between the flume and the underdrain.
Description of Related Art
Gravity filtration systems use a filter media to remove impurities from water. The main components of gravity filters are filter media and underdrain blocks. Underdrain blocks are generally square or rectangular in cross section and may have a long longitudinal axis as compared to their cross section. They are attached end-to-end to form sections called laterals. The filter media sit atop the underdrain blocks.
In practice, the gravity filtration system works by introducing the solution to be filtered above the filter media. Gravity causes the solution to pass vertically downward through the filter media and into the underdrain block. The underdrain block channels the filtered fluid, which has passed through the filter media, through the underdrain block interior and away from the filter.
Gravity filtration systems must be periodically backwashed with water and/or air. However, it can be difficult to create passages for proper distribution of the air and water between the flume and underdrain, or, in some cases, to prevent air from entering the flume from the underdrain. The flume is the chamber for distribution of backwash water and sometimes air and for collection of filtered water.
The problem of creating passages is usually associated with the geometry or low profile of the underdrain when the water opening is not large enough for a wall feed arrangement while preventing the passage of air from the underdrain into the flume.
Creating a large enough water opening is also difficult when the air-water interface is controlled at a low elevation near the bottom of the underdrain such that air is not restricted when passing through low openings between the flume and the underdrain.
Another problem often encountered is associated with fusion welding of the endplate to the underdrain block. Fusion welding often results in warpage and uneven surfaces, making it difficult to seal the endplate to the filter wall or orifice plate.
Yet another problem often encountered is associated with a dead zone, an area where no backwash water or air can be discharged during the backwashing process for cleaning of the filter media. Particularly, the dead zone can encompass a large area.